Post on 06-Jan-2016
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Sensory Processes3270
Lecture 4
KEYWORDS from Lecture 3Psychophysics
Fechner, Weber, Threshold, Method of limits, staircase, Method of constant stimuli, two alternative forced choice, method of adjustment
Signal detection theory, threshold as probability, sensitivity versus response bias, criterion, outcome matrix, hit/miss/false alarm or false positives/correct rejection, receiver operating characteristic curves (ROC curves), sensitivity, d-prime (d')
Just noticeable difference, Weber fraction/law/constant, Fechner's law, Stevens' power law, magnitude estimation, standard stimulus, response compression, response expansion
The difference threshold
just noticeable difference (jnd) Webers law (1834)the just noticeable increment is a constant fraction of the stimulusWeber FractionsTaste0.08 8% Brightness0.088% Loudness0.055% Vibration0.044% Line length0.033% Heaviness0.022% Electric shock0.011% Fechners law (1860)sensation magnitude proportional to logarithm (stimulus intensity)assumption: all jnds are the samestood for 100 years! Stevens law (1961)(To honour Fechner and repeal his law)sensation magnitude proportional to (stimulus intensity) raised to a power
Ernst Weber (1795-1878)Increase in intensityIntensity= constant
Gustav Fechner (1801-1887)Perceived magnitudeLog (intensity)
S.S. Stevens (1906-1973)Perceived magnitude(intensity) h
Consequences of Stevens Law
response compression response expansion linear on a log scale
Somatosensory System
section 3
Why?Perception--- body parts (proprioception)--- touch--- special --vibrissaeantennaepainbrailletemperatureProtectionTemperature regulationLimb arrangement and controlHead orientation (vestibular system)
How?ReceptorsNeural pathwaysNeural codes(remember those common features)
Coding in the somatosensory system detection
identify modality (Mller's doctrine of specific nerve energies 1826; labelled lines);
identify properties and spatial form
magnitude intensity (APs/sec; frequency coding; population coding; thresholds);
location (absolute, two-point discrimination, topographical coding)
movement
GLABROUS (non-hairy) SKINMEISSNERSCORPUSCLE(RA)MERKELSDISK (SA)RUFFINICORPUSCLE(SA)PACINICORPUSCLE(very RA)
MERKELSDISK (SA)Free nerveendingPACINICORPUSCLE(very RA)Nerve endingaround hair(RA)HAIRYSKINMEISSNERSCORPUSCLE(RA)RUFFINIENDING(SA)
SARARASA
RA SA very RA SA
stretchingvibrationfine detailhand grip control
SPATIAL EVENT PLOTSSA (Merkel)
RA (Meissner)
RA (Pacinian)
MERKEL (SA)PACINIAN (vRA)
SomatosensorypathwayDORSAL COLUMNSCROSS OVERIN BRAIN STEMVENTRAL POSTERIOR LATERALNucleus of the thalamusSOMATOSENSORY CORTEX
After a limb has been amputated, phantom sensations can sometimes be created by stroking other areas of skin.
Demonstrates: 1 plasticity, 2 Mllers law of specific nerve energies
Area of somatosensory cortex representing finger tipstimulate finger tip over many daysLarger area now devoted to this finger tip
DEMONSTRATESPLASTICITY
PRESSURETHRESHOLDSDont vary much
POINT LOCALIZATIONTHRESHOLDS
RECEPTIVE FIELDS ON THE ARM
Afferent fibresSARAPCCortical cells in area 3b (SA)
Lateral inhibition improves 2-point discrimination
Somatosensorypathways3a3b1254DORSAL COLUMNSCROSS OVER
3a3b1254Multiple representations
3a -- muscle spindles3b -- SA (cutaneous)1 ---- RA (cutaneous)2 ---- joints
LIMB SENSING ORGANSMuscle spindles, cutaneous mechanoreceptors and joint receptorscutaneous mechanoreceptorsMuscle spindlesJoint receptors
3a3b1254Multiple representations
3a -- muscle spindles3b -- SA (cutaneous)1 ---- RA (cutaneous)2 ---- joints
Secondary Somatosensory cortexSecondary Somatosensory cortexMultiple representations
3a -- muscle spindles3b -- SA (cutaneous)1 ---- RA (cutaneous)2 ---- joints
superior colliculus
SuperiorColliculus
SuperiorColliculus
Active vs passive touch
active objectpassive sensation
identifying cookies cuttersactive 95% correctpassive 49% correct
judged as samecould distinguishJUDGING TEXTURE
MeissnersRAPacinianvRAMeissnersRAPacinianvRAMeissnersRAPacinianvRASlow freqnoneHigh freqADAPT
chanceDEMONSTRATES THAT VIBRATION NEEDED FOR TEXTUREPOST-ADAPT
explore surface texture with tool
demonstrates use of vibration
haptic perception
Stereognosis: 3d object perception by haptic exploration
SARARASABARE NERVE ENDINGS
TEMPERATURE
Normal = 34Cold 5-40Warm 30-45Ratio (channel) codingParadoxical cold at high temps
PAIN
pain insensitivity = badreferred pain (eg. Angina to chest wall)sharp 1st followed by dull 2ndGATE theory (why rubbing helps)
To brainSlow pain fibresFast mechano-receptor fibres Closed by rubbing So pain stopped from going to brain... Normally held closed Opened by pain fibres
phantom limb painAcupunctureHypnosisExpectation (cognitive factors)endorphins and enkephalins (natural opiates)Naloxone (antagonist) makes pain worsealso reverses acupunctureendorphins up with stress..PAIN
pain insensitivity = badreferred pain (eg. Angina to chest wall)sharp 1st followed by dull 2ndGATE theory (why rubbing helps)
Sensation and Perception II3270
RevisionFor first midterm
Electrode, Microelectrode, Micron (1/1000th mm),membrane, nucleus, cytoplasm, Neuron, axon, dendrite, Schwann cell/glial cell, myelin sheath, node of Ranvier, Synapse, synaptic cleft, vesicle, neurotransmitter,receptors, ions, permeability, ion channels, voltage-dependent sodium channels, neural threshold, positive feedback, sodium (Na+), potassium (K+), sodium-potassium pump, electrochemical equilibrium potentials, sodium (Na+) +55mv, potassium (K+) -75mv, resting potential -70mv, polarization/ depolarization/ hyperpolarization, inhibitory post-synaptic potential (IPSP), Excitatory post-synaptic potential (EPSP),integration, axon hillock, action potential (AP), all-or-none, neuron threshold -55mv, saltatory propagation, AP propagationKEYWORDS from NEURAL BASIS
KEYWORDS from NEURAL BASIS modality (Mller's doctrine of specific nerve energies 1826; labelled line); intensity (APs/sec; frequency coding; population coding; thresholds); duration (rapidly and slowly adapting neurones) location (absolute, two-point discrimination, topographical coding)
Pacinian corpuscle
KEYWORDS from NEURAL BASISreceptive fields, thalamus, cortex, sulcus, gyrus, brainstem, topographic (maps) representation, superior colliculus, inferior colliculus (those are the names of the bumps on the brain stem that deal with vision and hearing respectively), Brodmann, phrenology,
areas of cortex: primary sensory areas (chemical, somatosensory, visual, auditory), motor cortex, association cortices (parietal, inferotemporal, frontal)
KEYWORDS from PSYCHOPHYSICSFechner, Weber, Threshold, Method of limits, staircase, Method of constant stimuli, two alternative forced choice, method of adjustment
Signal detection theory, threshold as probability, sensitivity versus response bias, criterion, outcome matrix, hit/miss/false alarm or false positives/correct rejection, receiver operating characteristic curves (ROC curves), sensitivity
Just noticeable difference, Weber fraction/law/constant, Fechner's law, Stevens' power law, magnitude estimation, standard stimulus, response compression.
Receptors, hairy/glabrous skin, rapidly/slowly adapting (RA/SA), transduction, Meissner's corpuscles (RA), Merkel's discs (SA),Nerve ending around hair (RA), Pacinian corpuscle (RA), Ruffini Ending (SA), free nerve endings, receptive fields, dorsal root, dorsal columns, dorsal column nuclei, trigeminal nerve, thalamus, somatosensory cortex, homunculus, somatotopic representation/map
spatial event plots, lateral inhibition, sharpening of receptive fields cortex, Brodmann areas 3a, 3b, 1, 2.
Joint detectors, muscle spindles, RAs, SAs, convergence
Secondary somatosensory cortexKeywords for SOMATOSENSORY SYSTEM
KEYWORDS from SOMATOSENSORY
1 detection 2 identify (modality) 3 identify (properties, spatial form) 4 magnitude 5 location 6 movement which fibre?, mapping of location, identifying modality/ sub-modality what pattern? frequency coding of magnitude
somatosensory psychophysics, detection thresholds, point threshold, two-point discrimination (larger than point thresholds because of need for unstimulated receptive field in between stimuli),
texture perception: vibration and active motion important
stereognosis, Haptic perception, variations over body surface, active touch/exploration, stereognosis, Aristotle's illusion,
Temperature
Pain (perception),
As promised .. The following is a question that will appear on the midterm next week (no, I did not promise to ANSWER it too.!GOOD LUCK!
A question from next weeks examThere will be 35 multiple choices: 1 point each = 91%There will be one label the diagram: 3.5 points= 9%Total = 38.5 points = 100%
Counts for 30% or 40% if it is your best.